#ifndef __FUNCTION__
#define __FUNCTION__
#include <iostream>
#include <cmath>
#include <algorithm>
#include <vector>

using namespace std;
class Function
{
 public:
  virtual double operator()(double _x) = 0;
  virtual double diff(double _x) = 0;
  virtual double diff2(double _x) = 0;
};
#endif